The objective optics used in most digital cameras are typically designed so as to minimize the optical point spread function (PSF) and maximize the modulation transfer function (MTF) of the optics, subject to the limitations of size, cost, aperture size, and other factors imposed by the camera manufacturer.
On the other hand, the optics in some imaging systems, such as certain digital cameras with extended depth of field, are intentionally designed in a manner that does not meet these criteria. For example, PCT International Publication WO 2007/054938, whose disclosure is incorporated herein by reference, describes an optical imaging assembly that may be used in a digital camera and is constructed so as to generate a distorted image at the imaging plane of the assembly. The digital camera incorporates a sensor at the imaging plane, and the distorted image formed on the sensor is corrected by a deconvolution engine so as to produce an undistorted image. The optical imaging assembly is configured to produce a high defocus aberration coefficient, greater than approximately 0.1, across the distorted image when the image is optimally focused to a focal plane of the assembly.
The high defocus aberration coefficient causes the MTF for the assembly to have generally equal low values for all objects in a large field, typically from infinity to approximately 10 cm from the assembly. Because of the equal values of the MTF at the different object distances within the field, the deconvolution engine may be configured to improve the MTF of all the images at the different object distances. The final images thus produced by the assembly and the deconvolution engine are substantially free of aberrations for all objects within the field, so that the digital camera has a large depth of field.